The ion-exchange of zeolites is well known in the art relating to zeolites. As equally well known is the difficulty of ion-exchanging certain zeolites with certain cations. Although the as-synthesized form of a given zeolite may have many uses, the ultimate use of a zeolite may be dependent on the ability to transform the as-synthesized zeolite to another form wherein at least a major portion of the zeolitic cations of the as-synthesized zeolite have been exchanged for another cation(s).
Unfortunately the cation exchange of certain zeolites, such as zeolites W and F, with specific cations is extremely difficult. For example, the as-prepared form of Zeolite W is generally associated with K.sup.+ cations when synthesized and Zeolite F is generally associated with K.sup.+ when synthesized. For many uses these cation forms of Zeolite W and Zeolite F are not acceptable and, accordingly, if such are to be employed in such uses they must be exchanged with a more acceptable cation.
The use of multi-step ion-exchange for ZSM-type zeolites and Zeolite Y is disclosed in U.S. Pat. Nos. 3,732,326 and 3,503,901, respectively. These patents employed a simple two step ion exchange procedure wherein the ZSM-type zeolite and zeolite Y were exchanged with NH.sub.4 Cl and then exchanged with Zn.sup.++ and Mn.sup.++, respectively. The relatively favorable nature of the exchange of these materials makes the exchange of these materials amenable to being carried out by use of relatively simple procedures, i.e., "by ion exchange with the non-metal cations using, for example, water soluble salts of the desired metal." (See: U.S. Pat. No. 3,503,901, column 4, lines 7 to 9).
The difficulties encountered in the cation exchange of certain zeolites when a desired cation is not as favorably accepted by the zeolite as the initial cation possessed by the zeolite are readily apparent when certain cation forms of zeolite F and zeolite W are to be prepared. Due to the nature of Zeolite F and Zeolite W the cation exchange of certain zeolitic cations associated therewith are not facilitated with the same ease as exchange for ZSM-type zeolites and zeolite Y. In U.S. Pat. No. 3,723,308 it is disclosed that zeolite F may be treated with a saturated calcium hydroxide solution which " . . . is effective in removing exchanged ammonium ion, even though the zeolite is capable of selectively imbibing the ammonium ion from a solution containing approximately equal amounts of ammonium and calcium ions." This preference for ammonium ions over calcium ions must be overcome if a high-level of Ca.sup.++ ion-exchange is to be achieved. The difficult nature of the exchange of an ammonium-exchange zeolite F with metal cations is exemplified by Example III of U.S. Pat. No. 3,723,308 wherein for an ammonium-exchanged Zeolite F only 33 percent of the ammonium ions were exchanged after regeneration. This low level of ion exchange for the ammonium ion is generally too low to be satisfactory for many uses where the presence of ammonium ions is a concern. Thus, except for uses such as waste water treatment and the like, a different method for treating Zeolite F must be employed wherein the unfavorable exchange of ammonium or other unfavorably exchanged cations will be facilitated.
Further, the exchange of Zeolite W with monovalent and divalent cations is disclosed in U.S. Pat. No. 3,012,853. The exchange of Zeolite W is disclosed as being effected by treatment of Zeolite W with a salt solution of the desired cation. The problems associated with such a procedure with respect to the exchange of specific cations is evident from a consideration of Table III of the patent. The treatment of the zeolite with a salt solution of calcium gave only an exchange of 52 percent and for lithium the exchange was only 22.6 percent. Since a high-level Ca.sup.++ exchange of the potassium form of Zeolite W may be the only suitable form for some uses of Zeolite W some method must be employed to increase the total percentage that calcium cations form of the total cations present in Zeolite W.
The use of a Na.sub.2 CO.sub.3 /NaOH solution at a pH of 11.0.+-.1.0 in a reclaiming process for crystalline zeolites, is disclosed in U.S. Pat. No. 4,122,007. This process is related to the sodium exchange of crystalline zeolites containing some ammonium cation. For the most part the crystalline zeolites reclaimed in this process contained alkali metal in the as-synthesized form and as a result had a high affinity for sodium cations. Thus, the process did not necessarily have to overcome an unfavorable exchange of the enchanged cation by the sodium cation.
The reaction of ammonium ions with a basic media to form ammonia is a know process and has been employed with clinoptilolite in the ammonium form to provide hydroxyl groups to clinoptilolite. The use of an alkaline regenerant solution is disclosed in U.S. patent application Ser. No. 485,401 for regeneration of ammonium containing zeolites with sodium or calcium ions with regeneration of the ammonium ions to ammonia.